Z-scan Measurement of the Upconversion Coefficient in Er:YAG

Solid-state laser research at the U.S. Army Research Laboratory (ARL) is currently emphasizing techniques for power scaling and achieving wavelengths in the eye-safer spectral region. We are studying erbium-doped yttrium aluminum garnet (Er:YAG), because it can be operated with a low quantum defect and has transitions around 1.6 ¿m. However, it suffers from cooperative pair upconversion, which can raise the lasing threshold, and thus lower the output power. In this report, we demonstrate how to measure the upconversion coefficient Cup using the z-scan technique with a continuous wave source. We find Cup to be proportional to [Er], for concentrations ranging from 0.5-5%. The value we find at 1% is 3.6¿10-17 cm3/s, approximately eight times larger than a value reported previously in the literature.